GUI_PrintRect
Callback that returns a rectangle object for the selected area.
###Callback Parameters
- Rect: Rectangle object with x,y,w,hparameters indicating the start point and the width and height of the rectangle in document coordinates.
Example:
RxCore.GUI_PrintRect.connect(function (rect) {
  var paperSize = {
    width: width,
    height: height,
    printrect: rect,
    mode: paper_orientation.mode,
  };
  RxCore.printSizeEx("printcanvas.htm", paperSize);
});